1. Field of the Invention
The invention relates to a bonding device, particularly for producing bond connections between electrical conductors made of wire material or strip material and contact points of substrates such as, in particular, electrical circuits, wherein the bonding device comprises a bonding head which can be rotated about a geometric axis of rotation, in particular a vertical axis, and on which a bonding tool and an ultrasonic transducer are disposed for ultrasonic vibration excitation of the bonding tool.
As is known such bonding devices perform in a way that by means of a bonding tool, that in a common embodiment could be a so-called wedge, an area of an electrical conductor that is to be bonded, e.g. an Aluminum or Gold wire, is pushed against the targeted contact point of a substrate, e.g. an electrical circuit, with a defined compressive force, while the bonding tool is performing ultrasonic oscillations perpendicular to the direction of the compressive force and transmits those oscillations into the conductor until a permanent so-called bond connection is established between the conductor and the contact point. For the excitation of the ultrasonic oscillation of the bonding tool so-called ultrasonic transducers are utilized, that typically use stacks of plate-shaped piezo elements as oscillation drivers. The piezo elements are usually connected to an alternating voltage such that the piezo elements perform consecutive elongations and contractions predominantly perpendicular to the planes of the plates and therefore in the longitudinal direction of the piezo element stack. These periodical alternations of length usually excite the tool holder of the bonding tool to perform longitudinal mechanical oscillations in the direction of the periodical alternations of length. As tool holder often a conically reducing horn that elongates into the same direction is utilized with the bonding tool attached to its tip, e.g. by means of a clamping screw, such that the longitudinal axis of the tool is perpendicular to the longitudinal axis of the transducer, i.e. perpendicular to the direction of the oscillation. As a result the tip of the tool also performs an oscillating movement transverse to the tool's longitudinal axis that is utilized to produce a bond connection. Bonding devices with ultrasonic transducers provide numerous advantages and are used in a multitude of applications. Frequently there is a requirement to produce a number of bond connections within a small area, wherein the so-called bonding head, i.e. the subassembly of the bonding device containing the bonding tool and the ultrasonic transducer (as well as usually a wire guide and as the case my be for so-called thick wire bonders a cutting tool) are mounted, needs to perform quick rotary motions around a vertically oriented geometrical axis of rotation. The fact that a conventional ultrasonic transducer equipped with a bonding head due to its function and hence its design exhibits a large mass moment of inertia is regarded as a constraining factor, hampering the rotation of the bonding head and accordingly requires large rotary drives.
2. Description of the Related Art
In this context it is the objective of the invention to further develop a bonding device of the aforementioned kind such that particularly the disadvantages described above are largely avoided.